The present invention relates in general to communications using Internet Protocol (IP) to share the load of Signaling System 7 (SS7) traffic in a distributed network. More particularly, the invention relates to transporting SS7 signaling traffic over an IP network using shared point codes without impeding SS7 Signal Control Connection Part (SCCP) functionality.
Internet Protocol (IP) has become a popular communications standard enjoying wide deployment and use. For example, the internet is now a worldwide network of communications equipment and service providers which use IP as a common signaling protocol for communicating. On the internet, messages are transmitted from one user to another over a vast infrastructure of routers, servers, gateways and communication devices. Typically, users on either end of the network operate computers equipped with appropriate software and equipment. The underlying link level protocols handle the messaging functions on both ends of the communication channel.
A popular protocol choice for telephony is a form of common channel signaling called Signaling System number 7 (SS7), which is a global standard for telecommunications defined by the International Telecommunication Union (ITU) and specifically the Telecommunications Standardization Section of the ITU (ITU-T). While IP networks communicate using flexible and easily modifiable connections, SS7 uses a dedicated network to carry signaling traffic. In essence, the SS7 standard defines the procedures and protocols by which network elements in the public switch telephone network (PSTN) exchange information over a digital signaling network including wireless (e.g. cellular), and wireline call setup, routing and control. The ITU definition of SS7 allows for variance of the procedures and protocols such as those promulgated by the American National Standards Institute (ANSI) and Bell Communications Research (Bellcore) standards used in North America as well as the European Telecommunication Standards Institute (ETSI) standards used in Europe.
Essentially, an SS7 network and the defined protocols are used for implementing call signaling functions including basic call setup management and tear down. In addition, SS7 specifies various wireless services such as personal communication services (PCS), wireless roaming and mobile subscription authentication. Recently, the SS7 protocol has been used for local number portability (LNP) as well as toll free and toll wireline services. Other services that benefit from the SS7 protocol include enhanced call features such as call forwarding, calling party name and number display and three way calling as well as a wide array of emerging applications standards that provide for efficient and secure worldwide telecommunication.
With an SS7 network, messages are exchanged between network elements over 56 or 64 kilobits per second (kbps) using bi-directional channels called signaling links. Signaling occurs-out-of-band on dedicated channels rather than in-band on voice channels. Compared to in-band signaling, out-of-band signaling provides faster call setup times, more efficient use of voice circuits, and support for intelligent network services which require signaling to network elements without voice trunks. In addition, out-of-band signaling provides for improved control over fraudulent network use.
Currently, SS7 requires a dedicated network for the transport of signaling traffic. Due to the high cost of building SS7 networks there is a strong motivation to use alternative, cheaper technology like Internet Protocol (IP) to using IP networks to carry SS7 traffic. In particular, the IETF SIGTRAN working group has developed a suite of protocols to carry SS7 traffic over an IP network. The M3UA (MTP3 User Adaptation) protocol, in particular, can be used to carry MTP3 level SS7 traffic transparently over an IP network. In this usage, a Signaling Gateway (SGW) network element is used to convert MTP3 traffic running over SS7 links into M3UA traffic over an IP network.
In particular, an IP network can be used to replace a large SS7 transit network at a lower cost. In this scenario, SS7 network elements are each connected to an SS7 Gateway, and SS7 Gateways communicate with each other over IP. The SS7 network elements communicate with each other using standard SS7 protocols, the SS7 Gateways transparently route the messages over IP. These SS7 Gateways then become xe2x80x9cSTP replacement gatewaysxe2x80x9d in the sense that they perform the role of a traditional SS7 Signal Transfer Point (STP). One example of such a system is xe2x80x9cSS7 Transport Over IP,xe2x80x9d available from Ericsson, Inc.
A problem faced by non-ANSI SS7 network operators is a shortage of available point codes. This is directly related to the small point code field allowed in ITU networks: 14 bit point codes allow only 16384 distinct point codes. With SS7 transport over IP, it is possible for the signaling gateway nodes to xe2x80x9csharexe2x80x9d the same point code on opposite side of the IP network. The SS7 nodes on each side of the IP network see the shared point code gateways as one virtual STP that happens to be geographically distributed.
A specific problem with point code sharing arises with the use of the SS7 SCCP protocol. SCCP has a management function which tracks the availability of SCCP functions in the network. When point codes are shared, the SCCP protocol has no way to keep the SCCP management functions updated in all SS7 gateways that share point codes, since the SS7 protocols were not designed to work when a point code has been reused, and the SCCP functionality is thus replicated. Since SS7/SCCP does not include the concept of point code reuse, the protocol is effectively unusable. Since SCCP is used to provide global title translation (GTT), a crucial function in SS7 networks, this could be considered a severe drawback of the point code sharing scheme.
What is needed in the art is a solution that enables a set of SS7 over IP Signaling Gateways to share point codes while continuing to provide global title translation functions.
In general, the present invention provides a method, system and device for increasing the efficiency of distributed networks and for enabling SS7-over-IP signaling gateways to share point codes without loss of SS7 functionality.
According to one aspect of the invention, a method is provided for use in a distributed network system using SS7 elements that communicate over an IP (Internet Protocol) network through IP signaling gateways adapted to share point codes. The method includes the support of Signaling Connection Control Part (SCCP) management functions across the distributed network system. Steps include transmission of a status query message to an SS7 element by a non-authoritative signaling gateway and receipt of the status query message at an intervening authoritative signaling gateway. The authoritative signaling gateway responds to the status query message including an indication of one or more subsystems in the system which are allowed or prohibited as reported by the SCCP management functions of an SS7 element of the system.
According to preferred embodiments of the invention, Global Title Translation (GTT) functionality is provided to an IP signaling gateway.
According to another aspect of the invention, a telecommunications system for supporting Signaling Connection Control Part (SCCP) management functions in a distributed network using shared point codes is provided. Subsystems in a distributed network are adapted to send status indications to elements of the network. The system is configured to transmit status queries and responses among SS7 and IP gateways of the distributed network.
According to yet another aspect of the invention, an SS7 system manager is provided for use in a distributed network. A plurality of SS7 signaling gateways are configured to support sharing of point codes across an Internet Protocol (IP) network. At least one authoritative SS7 signaling gateway is adapted to transmit Signaling Connection Control Part (SCCP) management functions of subsystems for receipt by a Network Interface Function (NIF), defined in the M3UA protocol known in the art. The NIF is adapted to receive SCCP management functions from the authoritative SS7 gateway and for broadcasting notification of subsystem state changes to the plurality of SS7 signaling gateways across the IP network. Preferably a subsystem table is also provided and is updateable by the NIF for storing indications of subsystem states.
The invention provides several technical advantages including enabling gateways with shared point codes to continue to provide Global Title Translation (GTT) functions. An additional advantage is that standard SCCP protocol stacks may be used to support shared point codes and IP network interworking. Moreover, shared point code gateways are enabled to correctly interwork with existing SCCP management functions in the SS7 portion of a distributed network and the SS7 nodes are able to receive correct SCCP management responses even though the point codes are being shared.